Field of the Invention
The present invention relates to the technical field of fingerprint identification, and in particular, relates to a fingerprint identification sensor and a terminal device.
Description of the Related Art
The fingerprint identification technology is widely applied in the field of the electronic security, and is a reliable method for implementing identity authentication. A capacitive fingerprint identification sensor is one of the widely used fingerprint sensors, and is formed by a miniaturized capacitor polar plate array. An upper surface of the polar plate is covered by an insulation plate, and when a user puts his or her finger on the insulation plate, the skin forms the other plate of a capacitor array. Since the distances between ridges and valleys of fingerprints in different zones and the capacitance plate array are different, such that capacitance of each capacitor polar plate varies accordingly. In this way, a fingerprint image is acquired.
FIG. 1 illustrates a common capacitive fingerprint identification sensor, which comprises a sensor unit, a driving amplifier 101, a driving metal ring 103 and a power supply (not illustrated in FIG. 1) supplying power for the sensor unit. The sensor unit comprises a capacitor array formed by a plurality of capacitor induction units 102, and FIG. 1 schematically illustrates any one of the plurality of capacitor induction units 102. The sensor unit outputs a driving signal to the driving amplifier 101, and the driving amplifier 101 amplifies the driving signal and outputs the amplified driving signal to the driving metal ring 103. When a finger 104 presses the capacitor array of the sensor unit, a coupling capacitance between the finger and the capacitor induction units 102 is CX. The driving signal is coupled to the finger through a capacitance CT from the driving metal ring 103, the capacitance CX between ridges and valleys of fingerprints in different zones and the capacitor induction units 102 varies, and the capacitor induction units 102 detects that the voltage varies accordingly. In this way, the fingerprint image is acquired.
The fingerprint identification sensor having this structure needs an external metal ring 103. However, to enlarge capacitance CT as large as possible, and reduce signal attenuation, the region where the fingerprint identification sensor is located needs to be hollowed out to place the metal ring 103, such that the finger may directly touch the metal ring 103. However, in some application scenarios, for example, the appearance design of a mobile phone and a tablet personal computer, to achieve mirror-like screen effect and improve water proof performance, it is not suitable to open a hole on the screen, which restricts the application scope of the fingerprint identification sensor.
In addition, an equivalent capacitance formed by series connection of a capacitance CS and a capacitance CM, in which CS is formed between a terminal device equipped with the fingerprint identification sensor and the ground, and CM is formed between the human body and the ground, and a capacitance CH, formed directly between the human body and the terminal device will cause attenuation to the driving signal on the driving metal ring 103. When the terminal device is provided with a metal housing, and the device is held in one user's hand, the attenuation to the driving signal will be more serious, thereby reducing clarity of the fingerprint image, and affecting the fingerprint identification effect.